The primary argument is usually the fact women can get laid even if they're disabled or ugly, unless they're in the bottom % of subhumans, but viewing it through that lens is mainly male centric and women are vastly different than males, so it's kind of a meaningless comparison to me. Women aren't as sex motivated as men are, so most "femcels" are based off of romance-based prospects rather than sexual ones, e.g. feeling like they'll never find true fulfilling and/or emotionally satisfying types of relationships, I imagine a big aspect of it is them assuming their appearance plays a part in it.